Spa shell



FIG. 1 is a perspective view of a spa shell showing our new design;

FIG. 2 is a second perspective view thereof;

FIG. 3 is a third perspective view thereof;

FIG. 4 is a fourth perspective view thereof; and,

FIG. 5 is a top plan view thereof.

The broken line portions show unclaimed subject matter only and form no part of the claimed design. 

CLAIM The ornamental design for a spa shell, as shown and described. 